Multi-pass touch contact tracking

ABSTRACT

In embodiments of multi-pass touch contact tracking, touch input sensor data is recognized as a series of components of a contact on a touch-screen display. The components can be determined to correlate to the contact based on multi-pass nearest-neighbor contact mapping that includes forward nearest-neighbor contact mapping of the components and reverse nearest-neighbor contact mapping of the components. The components can then be associated to represent a tracking of the contact. Subsequent components of the contact can also be determined and associated with the previous components of the contact to further represent the tracking of the contact.

RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 61/449,538 filed Mar. 04, 2011 entitled “Multi-Pass Touch ContactTracking” to Zhao et al., the disclosure of which is incorporated byreference herein in its entirety.

BACKGROUND

Portable computing devices, such as mobile phones, portable and tabletcomputers, entertainment devices, handheld navigation devices, and thelike increasingly offer more functions and features which can make itdifficult for a user to navigate and select commands that are relevantto a function the user wants to initiate on a device. In addition to thetraditional techniques used to interact with computing devices, such asa mouse, keyboard, and other input devices, touch sensors andtouch-screen displays are commonly integrated in mobile phones andtablet computers, and are utilized both for display and user-selectabletouch and gesture inputs. A continuing design challenge with these typesof portable devices having touch sensors and/or touch-screen displays isthe touch signal processing to track touch and gesture inputs that areidentified from successive frames of sensor image data. Touch contactson a touch-screen display represent the motion trace of a gesture, suchas when a user uses his or her fingers to contact a touch-screen displayand gesture while maintaining the contact with the display. A failure tocorrectly track and interpret the motion trace of a touch contact for agesture input can lead to the failure of gesture recognition operationsand gesture tracking processing.

For a gesture motion that is a relatively small or short gesture,conventional tracking processing may statically match the spatiallyco-located touch contacts from successive frames. However, this approachis not effective for a gesture motion that is a relatively large or longgesture, such as may be typically used on a tablet computer or othertype of slate form factor where fast gestures such as flicker or panningare involved. The tracking processing may not be sensitive to thecomplete motion of a gesture, which can result in a gesture “break”,which may then be recognized and processed as much shorter motion rangesthan the actual gesture motion. Alternatively, if the trackingprocessing is overly sensitive to the gesture motion, this can lead tomis-tracking the touch contacts, such as when a user inputs text with asoft or virtual keyboard that is displayed on a touch-screen display.

SUMMARY

This Summary introduces simplified concepts of multi-pass touch contacttracking, and the concepts are further described below in the DetailedDescription and/or shown in the Figures. This Summary should not beconsidered to describe essential features of the claimed subject matter,nor used to determine or limit the scope of the claimed subject matter.

Multi-pass touch contact tracking is described. In embodiments, touchinput sensor data is recognized as a series of components of a contacton a touch-screen display. The components can be determined to correlateto the contact based on multi-pass nearest-neighbor contact mapping thatincludes forward nearest-neighbor contact mapping of the components andreverse nearest-neighbor contact mapping of the components. The reversenearest-neighbor contact mapping is initiated when unmapped componentsremain after the forward nearest-neighbor contact mapping. Thecomponents can then be associated to represent a tracking of thecontact. Subsequent components of the contact can also be determined andassociated with the previous components of the contact to furtherrepresent the tracking of the contact.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of multi-pass touch contact tracking are described withreference to the following Figures. The same numbers may be usedthroughout to reference like features and components that are shown inthe Figures:

FIG. 1 illustrates an example system in which embodiments of multi-passtouch contact tracking can be implemented.

FIG. 2 illustrates example method(s) of multi-pass touch contacttracking in accordance with one or more embodiments.

FIG. 3 illustrates an example architecture of a contact tracking servicein accordance with one or more embodiments.

FIG. 4 illustrates an example architecture for processing multi-passtouch contact tracking in accordance with one or more embodiments.

FIG. 5 illustrates a high-level flow diagram for multi-pass touchcontact tracking in accordance with one or more embodiments.

FIG. 6 illustrates another flow diagram for multi-pass touch contacttracking in accordance with one or more embodiments.

FIG. 7 illustrates an example of multi-pass nearest-neighbor contactmapping in accordance with one or more embodiments.

FIG. 8 illustrates an example of motion prediction for a decision regionin accordance with one or more embodiments.

FIG. 9 illustrates an example of min-max distance determination for amultiple level maximum distance determination in accordance with one ormore embodiments.

FIG. 10 illustrates an example of crossing trajectories that mayindicate unwanted component associations in accordance with one or moreembodiments.

FIG. 11 illustrates an example of how to compute and account forcrossing trajectories as shown in FIG. 9 in accordance with one or moreembodiments.

FIG. 12 illustrates example method(s) of multi-pass touch contacttracking in accordance with one or more embodiments.

FIG. 13 illustrates various components of an example device that canimplement embodiments of multi-pass touch contact tracking.

DETAILED DESCRIPTION

Embodiments of multi-pass touch contact tracking are described. As notedabove, touch and gesture inputs on a touch-screen display of a computingdevice, such as a mobile phone or portable computer, may not beaccurately tracked and/or processed. Multi-pass touch contact trackinguses the prediction of components at touch positions from previousframes, and the tracking can be reliably achieved in the case of highmotion while at the same time, mis-tracking in the case of a softkeyboard can be avoided. Touch contact tracking can be based on thepredicted positions of previously identified components of a contact,with a set of rules defining the scope of validity of the trackingobtained by the prediction. In embodiments, multi-pass contact trackingis implemented for contact tracking with prediction based onnearest-neighbor distance matching (e.g., an algorithm or procedure),and a technique is implemented for nearest-neighbor distance matching inboth forward and reverse directions.

Touch signal processing involves tracing the touch contacts identifiedfrom successive frames of touch input sensor data. When the motion ofthe touch contacts are relatively high, a prediction via a min-maxdistance determination can be implemented to sort the maximum distancesin different permutations of the possible component mappings fordifferent finger contacts of a multi-finger gesture input. Thecomputational cost is proportional to N!, where N is the number offingers used for the gesture input. This may be prohibitive when the Nis more than ten fingers, such as when two or more users are interactingwith a touch-screen and/or playing a game. An alternative solutionimplements forward and reverse passes (e.g., multi-pass)nearest-neighbor distance matching.

The tracking accuracy and results are comparable to the min-max distancedetermination technique when the motion velocity is smaller, and thecomputational cost is proportional to N² instead of N!, which is lessprocessing intensive. Embodiments provide a solution of computing thecontact tracking with the multi-pass solution based on thenearest-neighbor distance matching in both the forward and reversedirections, such as when the prediction of the contacts from theprevious frames are well-defined. In the event that a prediction doesnot exist, the original solution to initiate the prediction via min-maxdistance determination can still be applied. Alternately, some limitingapproach can be implemented to avoid the min-max scheme altogether.

Embodiments of multi-pass touch contact tracking can include aprediction based two-level procedure for component identification andcontact tracking. A first-level of procedure is used to establish aninitial association of components of a contact for gesture inputtracking based on a prediction, and a second level of procedure is usedto validate based on a nearest-neighbor contact mapping criteria togenerate a final association of the components of a contact. Alsorelated is a set of rules defining the operations for multi-finger touchand gesture recognition. This may be implemented for any slate baseddevice, tablet device, mobile phone or computer with a touch-screendisplay, as well as for other similar technologies such as surface,indirect touch, etc.

While features and concepts of multi-pass touch contact tracking can beimplemented in any number of different devices, systems, environments,networks, and/or configurations, embodiments of multi-pass touch contacttracking are described in the context of the following example devices,systems, and methods.

FIG. 1 illustrates an example system 100 in which various embodiments ofmulti-pass touch contact tracking can be implemented. The example systemincludes a computing device 102, which may be any one or combination ofa mobile phone 104, entertainment device, navigation device, userdevice, wireless device, portable device, tablet computer 106,dual-screen folding device 108, and the like. The computing deviceincludes an integrated touch-screen display 110, which is implemented tosense a gesture input 112, such as a user-initiated gesture in a userinterface that is displayed on the touch-screen display. In thisexample, the gesture input is a two finger gesture across thetouch-screen display in an approximate direction indicated by the arrow,but may be a single finger gesture input, or a multi-finger gestureinput (e.g., three or more finger gesture input). Any of the computingdevices can be implemented with various components, such as one or moreprocessors and memory devices, as well as any number and combination ofdiffering components as further described with reference to the exampledevice shown in FIG. 13 to implement embodiments of multi-pass touchcontact tracking.

In the example system 100, the computing device 102 includes a touchinput module 114 (e.g., a lower layer component) that is implemented torecognize touch input sensor data 116 as the gesture input 112 on thetouch-screen display 110. The computing device also includes a gesturerecognition application 118 (e.g., a higher layer component) thatreceives the touch input sensor data from the touch input module as HIDreports 120 (i.e., human interface device reports). The HID reportsinclude a time and position data, as well as determined touch contacttracking, that correlates to gesture inputs on the touch-screen displayof the computing device. The gesture recognition application 118 isimplemented to recognize and generate various gestures as determinedfrom touch input data (e.g. the HID reports 120) associated with inputsor combinations of inputs, such as the gesture input 112. The gesturerecognition application can generate various gestures, such as selectgestures, hold gestures, motion gestures, tap gestures, and other typesof gestures from various user-selectable inputs.

An input recognition system of the computing device 102 may include anytype of input detection features and/or devices to distinguish thevarious types of inputs, such as sensors (capacitive or resistive),light sensing pixels, touch sensors, cameras, and/or a natural userinterface that interprets user interactions, gestures, inputs, andmotions. In implementations, the input recognition system can detectmotion inputs from discernable variables, such as from a directionvariable, from start region position variables and end region positionvariables, and/or from a motion rate variable (e.g., a particular numberof pixels per second).

As described herein, a gesture input may be recognized as a user inputwith one or more fingers on a touch-screen display of a device, and thegesture input includes one or more contacts that each correlate to theinput of a finger on the touch-screen display. In the FIG. 1 example,the two-finger gesture input 112 includes two contacts identified as afirst contact 122 that correlates to a first finger of the gestureinput, and a second contact 124 that correlates to a second finger ofthe gesture input.

The gesture input data is received as a series of frames, and a frameincludes a component that represents one touch position of a contact(e.g., along a gesture input that is one finger). For a two-fingergesture input, a frame can include a component of a first contact thatcorrelates to the input of a first finger, and include a component of asecond contact that correlates to the input of a second finger (and soon for more than a two-finger gesture input).

In the FIG. 1 example, the first contact 122 of the gesture input 112includes successive components, such as component 126, component 128,and component 130 at different touch positions along the first contact.Similarly, the second contact 124 of the gesture input 112 includessuccessive components, such as component 132, component 134, andcomponent 136 at different touch positions along the second contact.Accordingly, a first frame of the two-finger gesture input includes thecomponent 126 and the component 132 of the respective first and secondcontacts at N-2 in the series of components. Similarly, a next frame ofthe gesture input at N-1 includes the component 128 and the component134 of the respective first and second contacts, and a current frame ofthe gesture input at N includes the component 130 and the component 136of the respective first and second contacts.

Therefore, a contact of a gesture input spans multiple frames andincludes the components from each successive frame that have beenidentified as correlating to the contact, or to a section of thecontact. A component represents a touch position of a contact in a frame(e.g., after the component has been identified as correlating to thecontact). As described in embodiments, a component can be identified ascorrelating to a particular contact based on a nearest-neighbor contactmapping criteria that evaluates distance between component positions.However, if the nearest-neighbor contact mapping does not identify acomponent to one of the existing contacts, then a new contact of thegesture input can be generated to represent the tracking of anadditional finger used to gesture on the touch-screen display.

The touch input module 114 recognizes the touch input sensor data 116 asthe series of components of the two contacts 122, 124 of the gestureinput 112 on the touch-screen display 110 of the computing device 102.In embodiments, the touch input module 114 is implemented to generate asensor map 138 from the touch input sensor data 116 for each componentof each contact. A sensor map represents an individual component of acontact, such as when a user initiates the gesture input 112 on thetouch-screen display 110. In this example, the sensor map includeselements 140 shown as 8-bit hex values that represent the signalstrength at an element position in the sensor map. A stronger sensorsignal of the touch input sensor data indicates more touch contact withan element in the sensor map. The sensor map can be generated as atwo-dimensional array, and array indices of the elements in thetwo-dimensional grid correlate to sensed touch contact from the gestureinput on the touch-screen display. The stationary baseline level can besubtracted out so that the elements in an area around the sensor mapthat are not detected as part of the touch contact are normalized to azero level.

The computing device 102 also includes a contact tracking service 142that is implemented to determine predicted touch contact tracking 144that corresponds to one or more contacts of a gesture input on thetouch-screen display 110, such as the gesture input 112. The contacttracking service can be implemented as computer-executable instructions,such as a software application, and executed by one or more processorsto implement the various embodiments described herein. The contacttracking service can also be implemented as firmware on dedicated sensordevice hardware in the computing device. In this example, the contacttracking service is shown implemented as a component of the touch inputmodule 114. Alternatively, the contact tracking service may beimplemented as an independent software application or service to predicttouch contact tracking.

In embodiments, the contact tracking service 142 is implemented toperform various procedures and/or algorithms of multi-pass touch contacttracking. The contact tracking service can identify and predictcomponents of the gesture input that are mapped (e.g., correlated,associated) as the two contacts. The components 126-130 represent atracking of the first contact 122, and the components 132-136 representa tracking of the second contact 124. The components that are identifiedas correlating to a particular contact are all assigned the sameidentifier. For example, the components 126-130 of the first contact 122are all assigned the same first identifier, and the components 132-136of the second contact 124 are all assigned the same second identifier,where the first and second identifiers are different to distinguish theseparate contacts. As further described below, the contact trackingservice can validate that a predicted component position correlates to asubsequent component of a contact based on a nearest-neighbor criteriathat evaluates distance from the predicted component position to theadditional components of the contact. Additionally, the contact trackingservice can determine that components correlate to a particular contactbased on a min-max distance determination between the components of thecontact.

Example methods 200 and 1200 are described with reference to respectiveFIGS. 2 and 12 in accordance with one or more embodiments of multi-passtouch contact tracking. Generally, any of the services, functions,methods, procedures, components, and modules described herein can beimplemented using software, firmware, hardware (e.g., fixed logiccircuitry), manual processing, or any combination thereof. A softwareimplementation represents program code that performs specified taskswhen executed by a computer processor. The example methods may bedescribed in the general context of computer-executable instructions,which can include software, applications, routines, programs, objects,components, data structures, procedures, modules, functions, and thelike. The program code can be stored in one or more computer-readablestorage media devices, both local and/or remote to a computer processor.The methods may also be practiced in a distributed computing environmentby multiple computer devices. Further, the features described herein areplatform-independent and can be implemented on a variety of computingplatforms having a variety of processors.

FIG. 2 illustrates example method(s) 200 of multi-pass touch contacttracking. The order in which the method blocks are described are notintended to be construed as a limitation, and any number of thedescribed method blocks can be combined in any order to implement amethod, or an alternate method.

At block 202, a gesture input is recognized on a touch-screen display.For example, the touch input module 114 (FIG. 1) at the computing device102 recognizes various inputs or combinations of inputs, such as thegesture input 112 on the touch-screen display 110 of the example device104. In this example, the gesture input 112 is a two-finger gestureinput that includes the two contacts identified as the first contact 122that correlates to a first finger of the gesture input, and the secondcontact 124 that correlates to the second finger of the gesture input.

At block 204, multi-pass touch contact tracking is determined thatcorresponds to the gesture input. At block 206, next component positionsof gesture input contacts is predicted based on one or more previouscomponents of the contacts. At block 208, a next component of thecontacts is predicted based on a forward nearest-neighbor contactmapping of the components of the contacts. At block 210, the nextcomponents of the contacts are predicted based on a reversenearest-neighbor contact mapping of the components of the contacts. Atblock 212, the components of each contact of the gesture input aremapped to represent a tracking of each of the contacts. At block 214, afinal association of the components of the contacts is validated basedon the forward and reverse nearest-neighbor contact mapping.

For example, the contact tracking service 142 (FIG. 1) at the computingdevice 102 determines multi-pass touch contact tracking that correspondsto the gesture input 112 on the touch-screen display 110 of the exampledevice 104. The contact tracking service also predicts next componentpositions of gesture input contacts based on a forward nearest-neighborcontact mapping of the components of the contacts; predicts the nextcomponents of the contacts based on reverse nearest-neighbor contactmapping of the components of the contacts; maps (e.g., correlates,associates) the components of each contact of the gesture input torepresent a tracking of each of the contacts; and/or validates a finalassociation of the components of the contacts based on the forward andreverse nearest-neighbor contact mapping.

FIG. 3 illustrates an example implementation and various components ofthe contact tracking service 142 that is described with reference toFIG. 1, and which is implemented for touch signal processing. FIG. 4illustrates an example architecture 400 for processing multi-pass touchcontact tracking and is described with reference to the touch inputmodule 114 shown in FIG. 1, and with reference to the contact trackingservice 142 shown in FIGS. 1 and 3. FIG. 5 illustrates a high-level flowdiagram 500 of multi-pass touch contact tracking implemented by a touchcontact tracker module 300 (also referred to as the “contact tracker”)that is shown as a component of the contact tracking service 142 in FIG.3.

Touch input sensor data 116 is input at 402 (FIG. 4) (e.g., received atthe touch input module 114), and a sensor unit of the touch input modulegenerates sensor maps 302 (FIG. 3) from the touch input sensor data foreach component of a contact of a gesture input. A baseline level can besubtracted out, or otherwise removed, for elements around a sensor mapthat are normalized to a zero level at 404. For example, the sensor map138 can be generated as a two-dimensional grid with a pitch of 5 mm andan element depth of eight to sixteen bits. A connected componentsanalyzer 304 is implemented for connected component analysis at 406. Theconnected components analyzer receives the normalized sensor maps 420 asan input and generates an array 306 of the connected contact componentsthat represent the touch contacts replaced by components of a gestureinput. The touch contact tracker module 300 is implemented for componentidentification and contact tracking at 408 to associate (e.g., correlateor map) the components from previous frames and the components at touchpositions in a current frame that represent the traces (e.g., tracking)of a continuous gesture motion, such as the tracking of the firstcontact 122 and the tracking of the second contact 124.

In FIG. 5, a set of touch contacts from a previous frame are examinedfor predictability when each new frame is received as input at block502. Touch contacts that are still in the initial tracking stage (i.e.,“yes” from block 502), and before a sufficient history of touch contactassociation has been established, are input to a touch contact mapmodule 308 (also referred to as the “contact mapper”) for min-maxcontact mapping at block 504. The min-max contact mapping generates aninitial association of mapped contact components 310, which are thenoutput and buffered as determined components 312 with a history ofassociation for future frames.

Touch contacts that are not initial touch contacts (i.e., “no” fromblock 502), such as when at least two previous frames have beenreceived, are input to a motion prediction module 314 for motionprediction at block 506 to generate touch contact predicted positions316. These touch contact predicted positions, along with the connectedcomponents 508 of the current frame, are input into the touch contactmap module 308 for nearest-neighbor contact mapping at block 510, whichis based on the forward nearest-neighbor distance matching algorithm(e.g., procedure or determination). The result of the nearest-neighbordistance matching is checked against a criterion at 512 to determinewhether the components of the current frame have been successfullymapped to previous components of a contact.

If the mapping of the components is successful (i.e., “yes” from block512), then the mapped association is input to a touch contact mergermodule 318 at block 514. If the mapping of the components is notsuccessful (i.e., “no” from block 512), then the components are input tothe touch contact map module 308 for min-max contact mapping at block516 and a two-level combinatory mapping is invoked. With the input fromthe motion prediction module 314 (i.e., as output at block 506) and theconnected components 508, the min-max contact mapping attempts toestablish a first level nearest-neighbor association between these twosets of component positions based on a min-max distance determination,along with a set of rules involving hand and/or finger kinematicdynamics.

The min-max scheme can be implemented to compute the distances betweenall pairs of components in a potential matching. For a configurationwith N touch positions mapping to N components, the number of potentialmatching equals N! and for each match, a computation of the distancesand a sorting of its maximum distance is determined If the min-maxdistance determination is initiated when a forward nearest-neighbordistance determination fails to match components, a delay in processingmay be noticeable to the user as a glitch.

For those contacts that do not have a mapping established at the firstlevel (e.g., at block 518), they are routed over all of the componentsfor a contact aliasing check at block 520 to determine possiblealiasing, which may be merged contacts as determined at block 514 by thetouch contact merger module 318. A single component may associate tomultiple touch contact positions, which can occur when multiple fingersof a gesture input motion move closer to appear as a single componentbased on the touch input sensor data. To detect a touch contact merger,for any unmapped component after a first-level contact association, anearest-neighbor verification can be initiated for contact associationsfor all of the components, and any match indicates an aliasedassociation between a single component and multiple touch positions.

The touch contact merger module 318 processes and resolves the mergedcomponents, such as to independently check whether two touch positionshave the same [x,y] grid point coordinates. A contact merger may includemultiple touch positions aliased to one component, as well as a scenarioof merge-on-landing when a first touch position is already sensed ordetected as a first finger touches on a touch-screen display and a userlands a second finger closely next to the first one. The two touchpositions may then be detected as merged together in one largercomponent.

FIG. 6 illustrates another high-level flow diagram 600 of multi-passtouch contact tracking implemented by the touch contact tracker module300 (also referred to as the “contact tracker”) that is shown as acomponent of the contact tracking service 142 in FIG. 3. The examplediagram 600 is similar to the diagram 500 shown in FIG. 5, except thatthe three operations for the min-max mapping 516, the nearest-neighboreddecision for association 518, and the contact aliasing check at 520 arereplaced with a reverse nearest-neighbor contact mapping at 616.Additionally, the nearest-neighbor contact mapping at 510 is replacedwith a forward nearest-neighbored contact mapping at 610. A multi-passnearest-neighbor distance determination includes the forwardnearest-neighbor contact mapping of components and the reversenearest-neighbor contact mapping of the components.

FIG. 7 illustrates an example 700 of multi-pass nearest-neighbor contactmapping, such as applied to a two-finger gesture input that includes twocontacts identified as a first contact 702 that correlates to a firstfinger of the gesture input, and a second contact 704 that correlates toa second finger of the gesture input. The first contact 702 includessuccessive components, such as component A and component C at differenttouch positions along the first contact. Similarly, the second contact704 includes successive components, such as component B and component Dat different touch positions along the second contact. The operation offorward nearest-neighbored contact mapping 610 searches for a componentwhich is nearest to the predicted location of a contact. When suchcomponent is found and the distance to the prediction point of thecontact is smaller than a defined threshold, an association can beestablished to associate the component with the contact. Note that thedefined distance is not in a uniform metric, but rather is stretchedalong the direction of the velocity in order to compensate for thepossible inaccuracy caused by the prediction at high velocity.

A failure of the forward nearest-neighbor contact mapping can beattributed to the non-uniform nature of the distance used for anearest-neighbor distance determination. As shown in FIG. 7, thecomponent A is at a predicted position that should match to component Cof the first contact 702, and similarly, the component B is at apredicted position that should match to component D of the secondcontact 704. The dashed lines of the contacts represent avelocity-skewed metric for distance comparison. However, due toproximity, the forward nearest-neighbor contact mapping 610 would matchthe predicted position of component B with component C as shown at 706.The result of this forward nearest-neighbor contact mapping is that bothof the components A and B would be matched to component C as a 2-1contact merge, and the component D is left unmapped, which may then bedetermined as a beginning of a new contact, thus causing a contactmatching break of the contact 704.

In embodiments, the reverse nearest-neighbor contact mapping 616 isimplemented to resolve the situation of a component left unmapped, witha reverse pass after the forward nearest-neighbor matching pass. Thereverse pass starts with the unmapped component D, and determines thebest match from all of the other components in the contacts. Once anoptimal component match is determined, such as the component B in thisexample, all of the associations on component B that were previouslyestablished during the forward nearest-neighbor mapping are released.This results in newly unmapped components, such as component C, and thereverse nearest-neighbor contact mapping is applied to these newlyunmapped components in the reverse direction until there are no moreunmapped components.

The forward nearest-neighbor contact mapping is initiated at 610 foreach unmapped component to determine a matching contact. The result ofthe forward nearest-neighbor contact mapping is checked at 612 todetermine whether all of the unmapped components of the current framehave been successfully mapped to previous components of a contact. Ifthe mapping of the components is not successful (i.e., “no” from block612), then all of the component to contact mappings are disconnected(e.g., released) and the reverse nearest-neighbor contact mapping isinitiated at 616.

The use of processing resources for reverse nearest-neighbor contactmapping is minimal due to the proportional number of unmatchedcomponents. The propagation in the reverse direction is also minimal, asthe process correlates to the three or four fingers of a user's handstaying together and moving at a fast speed along with the directionthat the gesture input spans. For any components that are determined asunmapped due to a new finger making contact with the touch-screendisplay, the multi-pass touch contact tracking does not compromise thevalidity of the new contact as a new input because a newly determinedtouch contact is typically a distance far enough from the predictedtouch positions, and thus the reverse nearest-neighbor contact mappingwill exit after the first iteration.

FIG. 8 illustrates an example 800 of motion prediction for a decisionregion 802 that represents a predicted component position 804 of acontact given the tracking of the contact, such as a contact of thegesture input 112 on the touch-screen display 110 of the example device104 (FIG. 1). In embodiments, the motion prediction module 314 (FIG. 3)of the contact tracking service 142 is implemented for motion predictionwhen the gesture input begins on the touch-screen display at positionN-2 and continues the tracking of the contact to position N-1 and thento position N. The component at position N is determined as thecomponent that is associated with the components at N-2 and N-1 based onproximity to the predicted component position 804. When there is anassociation for a component identified as i in previous N-frames, thenthe position of the component in the current frame of X_(i) can bepredicted thru a linear combination of the previous component positionsof the contact, as in the following equation:

${\hat{X_{t}}(t)} = {\sum\limits_{k = 1}^{N}\; {a_{k}{X_{i}\left( {t - k} \right)}}}$

If N=3 for example, one solution is a constant a1=2.5, a2=−2, and a3=0.5determined via the simple constant acceleration condition. If N=2 forexample, then a solution is a1=2 and a2=−1. In general, thesecoefficients may be time-dependent variables and a more advancedtechnique, such as a Kalman filter, can be utilized to determine theparameters through an iterative procedure.

For each component {circumflex over (X)}₁(t) of the i^(th) touchposition generated in the prediction stage above, the nearest-neighborcontact mapping attempts to associate a component X(t) of the currentframe. A nearest-neighbor contact mapping can be resolved as describedherein and/or with other techniques and algorithms. A mapped associationcan be established when all of the components of a current frame areconsidered to determine a component with an X(t) that is within thetwo-dimensional decision region 802 centered around the predictedposition {circumflex over (X)}₁(t). The decision region can beconstructed first with a round shape of radius r which corresponds to anarea matching the actual touch shape of the ith contact at the framet-1. The round shape region is then modified with a velocity relatedexpansion along the direction of the velocity, and with an expansionfactor λ proportional to the norm of the velocity. This expansionaccounts for the error introduced by the inaccuracy of the velocityprediction. In general, λ can have an upper bound λ max to avoiderroneous association between fingers of a gesture input motion that areclose together along the direction of the velocity. In oneimplementation, λ=(1+λmax|v|)/(1+|v|), however other choices for λ arealso possible.

In practice, the procedure of verifying the nearest-neighbor contactmapping criterion can be performed in a reverse procedure. A differencevector: d=X(t)−{circumflex over (X)}₁(t) is computed first, and then areverse scaling on d is performed with the factor 1/λ along thedirection of velocity vector: v=X(t-1)−X(t-2). The norm of the resultantvector {tilde over (d)} is then checked against the radius r of thedecision region, and a value smaller than r indicates that anassociation has been determined Another extension of thenearest-neighbor contact mapping is to implement a probabilisticapproach, where a probability distribution function of the vector d isdefined, and instead of passing a hard decision of which touch thecomponent X(t) belongs to, a probability distribution is passed amongall of the components. This information can be passed through the HIDreports so that the gesture recognition application 118 (FIG. 1) (e.g.,a higher layer) can utilize the information.

In embodiments, criteria that nearest-neighbor contact mapping issuccessful can be established, such as to determine a successful mappingat block 512 (FIG. 5). Generally, the nearest-neighbor contact mappinggenerates a reliable touch component association. However, in somedistributions of touch contact velocity, an unreliable association maybe determined, such as when the velocities of the touch positionsinvolved are fast and with substantial acceleration in certaindirections. The resulting predicted component locations become closer tothat of neighbored components rather than the tracking contact componentthat should be associated with the predicted component.

A simple condition to detect this instance of an unreliable associationis to determine that the total number of unassociated components afterthe nearest-neighbor mapping is greater than the difference between thenumber of components and the number of touches. Note that this is asufficient condition in that, theoretically, there may be good mappingsclassified as a bad mapping. Since the majority of frames have reliableassociation predictions, the instances of an unreliable association(e.g., a failure case) will likely be of a very small percentage (e.g.,less than 5%) with a negligible computational cost. If a failure case isdetected, an algorithm or procedure for combinatory contact mapping canbe invoked to determine a correct association, as implemented by thetouch contact map module 308 of the contact tracking service.

The combinatory contact mapping can establish a reliable mapping betweena given set of contacts established in a previous frame and a given setof components in the current frame. When a prediction is determined andthe nearest-neighbor contact mapping fails, the combinatory contactmapping can be used to establish a first-level association between thetwo sets (e.g., the touch positions and the components) by matching theprediction residuals between the prediction positions and that of thecomponents. When a prediction is not determined at the initial phase ofa contact life span, the combinatory contact mapping can also be used toestablish the initial association. If an initial association of acontact does not exist, as may happen in the first two frames of a newcontact, the touch contact map module 308 can then set the originalposition as the predicted position, and no prediction residual ispresent. The touch contact map module can include the combinatorycontact mapping algorithm, the min-max distance determination algorithmfor distance mapping, and a cross-trajectory suppressor for penalizingtrajectories of gesture input motions that cross each other. Thecombinatory contact mapping algorithm can be implemented as describedherein via a min-max algorithm and/or with other techniques andalgorithms, such as the Hungarian Algorithm.

In embodiments, a nearest-neighbor verification for contact andcomponent association can be implemented. The first-level associationthat is established with a min-max distance determination (as furtherdescribed below) can be evaluated with a second-level verificationprocess, which is similar to nearest-neighbor contact mapping.Specifically the component X(t) of the current frame, after theestablishment of the initial association to {circumflex over (X)}_(l)(t)at the min-max mapping stage, is confirmed to belong to the i^(th)contact if X(t) falls into a two-dimensional predicted region centeredaround the predicted position {circumflex over (X)}_(l)(t) of the i^(th)contact. Generally, a difference to the nearest-neighbor contact mappingis that instead of evaluating all of the possible components for a given{circumflex over (X)}_(l)(t), a component with the first-levelassociation is selected for the verification process.

FIG. 9 illustrates an example 900 of min-max distance determination fora multiple level maximum distance determination. In embodiments, thetouch contact map module 308 (FIG. 3) of the contact tracking service142 is implemented to determine an optimal mapping to associate (e.g.,determine, correlate) the components of a previous frame to thecomponents of a current frame such that the maximum distance between allmapping pairs within the mapping is minimized. Depending on how themin-max distance determination is applied, the position of a componentof the previous frame that is being mapped from may be the predictedposition of a component in a subsequent frame.

The min-max distance determination seeks to determine the mapping thathas the smallest maximum distance between the components of a previousframe and the components of a current frame. In this example, a maximumdistance 902 from a component 904 to a touch position 906 of asubsequent component has already been identified. A mapping is thendetermined from components 908 in a current frame to components 910 in aprevious frame. For example, the determination for a first contact iswhether to select the component association represented by the dashedline or the solid line at 912, and the determination for a secondcontact is whether to select the component association represented bythe dashed line or the solid line at 914.

In an equation, P(i) defines a mapping from N to M where N representsthe set of numerical labels on the contacts from a previous frame, and Mrepresents the labels of the components in a current frame. Morespecifically, P(i) is a function of i ∈ N (range 0 . . . N-1) taking thevalue in M (range 0 . . . M-1), such that P(i)≠P(j) for i≠j.Furthermore, P denotes the entire set of all possible P(i), and the bestP(i) within P is determined so that the mapping defines an associationof current components with previous touch positions that makes the mostsense.

For any P(i) in P, an array D(i,P): i ∈ N denotes the distances for eachpair i in the mapping. More specifically, for each pair i in themapping, the distance D(i,P) is defined as the L² distance between theposition of the component of the current frame and the predictedposition of the component of the previous frame if the predictionexists, or the position of the component of the previous frame. Adescending sort of array of D(i,P) is then initiated and the result isdenoted as Sorted D(k,P), where 0≦k<N and:

SortedD(0, P)≧SortedD(1, P) . . . ≧SortedD(N−1, P)

The best P can be obtained when solving the following minimizationproblem: BestP=arg min_(P∈P)(ED(P)+λ₀*EC(P)); where:

${{ED}(P)}\overset{def}{=}{\sum\limits_{k = 1}^{N}\left( {{{SortedD}\left( {k,P} \right)}*{MAXD}^{N - k}} \right)}$

The value ED is the contribution from the maximum distance matching, andthe value MAXD is the maximum distance on the display screen (typicallythe diagonal distance). The layered maximum distance matching in thisexample accounts for the degeneracy of the configuration once thecomponents with larger distances have been matched.

FIG. 10 illustrates an example 1000 of crossing trajectories that mayindicate unwanted associations between components 1002 in a currentframe and components 1004 from a previous frame. A min-max distancedetermination may incorrectly associate a current component to aprevious component. A value EC(P) is defined as being proportional tothe number of crossings in trajectory for all pairs of labels in themapping P, and at a sampling rate of approximately 100 Hz, a crossingcan be regarded as spurious mapping. In this example, the matching ofcomponent A to component C, and component B to component D is preferredover the crossing trajectories of components A to D and B to C. However,without EC(P), a pure ED(p) would likely incorrectly associate thecrossing trajectories of components A to D and B to C, which is clearlyundesired.

FIG. 11 illustrates an example 1100 of how to compute and account forcrossing trajectories, such as shown in FIG. 10. A computation of ECconsiders that for the pair of trajectories x₀x₁ and x₂x₃ , thecondition where they cross each other is when the following inequalitieshold true simultaneously:

0<(b ₁ *c ₀ −b ₀ *c ₁)/det<1

0<(a ₀ *c ₁ −a ₁ *c ₀)/det<1

(det=b ₁ *a ₀ −b ₀ *a ₁); where

a=(a ₀ , a ₁)=x ₁ −x ₀

b=(b ₀ , b ₁)=x ₂ −x ₃

c=(c ₀ , c ₁)=x ₂ −x ₀

FIG. 12 illustrates example method(s) 1200 of multi-pass touch contacttracking. The order in which the method blocks are described are notintended to be construed as a limitation, and any number of thedescribed method blocks can be combined in any order to implement amethod, or an alternate method.

At block 1202, touch input sensor data is recognized as a series ofcomponents of a contact on a touch-screen display. For example, thetouch input module 114 (FIG. 1) at the computing device 102 recognizesthe touch input sensor data 116 as the series of components of a contact(e.g., either of the two contacts 122, 124) of the gesture input 112 onthe touch-screen display 110, such as on the example device 104.

At block 1204, the components are determined as correlating to thecontact based on multi-pass nearest-neighbor contact mapping. Forexample, the contact tracking service 142 (FIG. 1) at the computingdevice 102 determines that the components of the contact 122 correlateto the contact based on multi-pass nearest-neighbor contact mapping thatincludes forward nearest-neighbor contact mapping of the components andreverse nearest-neighbor contact mapping of the components.

At block 1206, the forward nearest-neighbor contact mapping isinitiated. For example, the content tracking service 142 initiates theforward nearest-neighbor contact mapping to evaluate distance from oneor more additional components of the contact to predicted componentpositions of the components. At block 1208, a determination is made asto whether any unmapped components remain after the forwardnearest-neighbor contact mapping. If unmapped components remain (i.e.,“yes” from block 1208), then at block 1210, mapped componentassociations that are mapped by the forward nearest-neighbor contactmapping are released and, at block 1212, the reverse nearest-neighborcontact mapping is initiated. For example, the content tracking service142 determines whether unmapped components remain after the forwardnearest-neighbor contact mapping and, if yes, releases any mappedcomponent associations and initiates the reverse nearest-neighborcontact mapping to evaluate distance from the predicted componentpositions to the one or more additional components of the contact.

At block 1214, the components of the contact are associated to representa tracking of the contact and, at block 1216, a same identifier is thenassigned to all of the components that are associated with the contact.For example, the contact tracking service 142 associates all of thecomponents of the contact to represent a tracking of the contact andassigns the same identifier to all of the components.

FIG. 13 illustrates various components of an example device 1300 thatcan be implemented as any of the devices, or services implemented bydevices, described with reference to the previous FIGS. 1-12. Inembodiments, the device may be implemented as any one or combination ofa fixed or mobile device, in any form of a consumer, computer, portable,user, communication, phone, navigation, television, appliance, gaming,media playback, and/or electronic device. The device may also beassociated with a user (i.e., a person) and/or an entity that operatesthe device such that a device describes logical devices that includeusers, software, firmware, hardware, and/or a combination of devices.

The device 1300 includes communication devices 1302 that enable wiredand/or wireless communication of device data 1304, such as receiveddata, data that is being received, data scheduled for broadcast, datapackets of the data, etc. The device data or other device content caninclude configuration settings of the device, media content stored onthe device, and/or information associated with a user of the device.Media content stored on the device can include any type of audio, video,and/or image data. The device includes one or more data inputs 1306 viawhich any type of data, media content, and/or inputs can be received,such as user-selectable inputs and any other type of audio, video,and/or image data received from any content and/or data source.

The device 1300 also includes communication interfaces 1308, such as anyone or more of a serial, parallel, network, or wireless interface. Thecommunication interfaces provide a connection and/or communication linksbetween the device and a communication network by which otherelectronic, computing, and communication devices communicate data withthe device.

The device 1300 includes one or more processors 1310 (e.g., any ofmicroprocessors, controllers, and the like) which process variouscomputer-executable instructions to control the operation of the device.Alternatively or in addition, the device can be implemented with any oneor combination of software, hardware, firmware, or fixed logic circuitrythat is implemented in connection with processing and control circuitswhich are generally identified at 1312. In embodiments, the device 1300can also include a touch input module 1314 that is implemented torecognize touch input sensor data. Although not shown, the device caninclude a system bus or data transfer system that couples the variouscomponents within the device. A system bus can include any one orcombination of different bus structures, such as a memory bus or memorycontroller, a peripheral bus, a universal serial bus, and/or a processoror local bus that utilizes any of a variety of bus architectures.

The device 1300 also includes one or more memory devices 1316 (e.g.,computer-readable storage media) that enable data storage, such asrandom access memory (RAM), non-volatile memory (e.g., read-only memory(ROM), flash memory, etc.), and a disk storage device. A disk storagedevice may be implemented as any type of magnetic or optical storagedevice, such as a hard disk drive, a recordable and/or rewriteable disc,and the like. The device may also include a mass storage media device.

Computer readable media can be any available medium or media that isaccessed by a computing device. By way of example, and not limitation,computer readable media may comprise storage media and communicationmedia. Storage media include volatile and non-volatile, removable andnon-removable media implemented in any method or technology for storageof information, such as computer-readable instructions, data structures,program modules, or other data. Storage media include, but are notlimited to, RAM, ROM, EEPROM, flash memory or other memory technology,CD-ROM, digital versatile disks (DVD) or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to storeinformation and which can be accessed by a computer.

Communication media typically embody computer-readable instructions,data structures, program modules, or other data in a modulated datasignal, such as carrier wave or other transport mechanism. Communicationmedia also include any information delivery media. A modulated datasignal has one or more of its characteristics set or changed in such amanner as to encode information in the signal. By way of example, andnot limitation, communication media include wired media such as a wirednetwork or direct-wired connection, and wireless media such as acoustic,RF, infrared, and other wireless media.

A memory device 1316 provides data storage mechanisms to store thedevice data 1304, other types of information and/or data, and variousdevice applications 1318. For example, an operating system 1320 can bemaintained as a software application with the memory device and executedon the processors. The device applications may also include a devicemanager, such as any form of a control application, softwareapplication, signal processing and control module, code that is nativeto a particular device, a hardware abstraction layer for a particulardevice, and so on. In this example, the device applications 1318 includea gesture recognition application 1322 and a contact tracking service1324 that implement embodiments of angular contact geometry as describedherein.

The device 1300 also includes an audio and/or video processing system1326 that generates audio data for an audio system 1328 and/or generatesdisplay data for a display system 1330. The audio system and/or thedisplay system may include any devices that process, display, and/orotherwise render audio, video, display, and/or image data. Display dataand audio signals can be communicated to an audio device and/or to adisplay device via an RF (radio frequency) link, S-video link, compositevideo link, component video link, DVI (digital video interface), analogaudio connection, or other similar communication link. Inimplementations, the audio system and/or the display system are externalcomponents to the device. Alternatively, the audio system and/or thedisplay system are integrated components of the example device, such asan integrated touch-screen display.

Although embodiments of multi-pass touch contact tracking have beendescribed in language specific to features and/or methods, the subjectof the appended claims is not necessarily limited to the specificfeatures or methods described. Rather, the specific features and methodsare disclosed as example implementations of multi-pass touch contacttracking.

1. A method, comprising: recognizing touch input sensor data as a seriesof components of a contact on a touch-screen display; determining thatthe components correlate to the contact based on multi-passnearest-neighbor contact mapping; and associating the components torepresent a tracking of the contact.
 2. A method as recited in claim 1,wherein the multi-pass nearest-neighbor contact mapping includes forwardnearest-neighbor contact mapping of the components and reversenearest-neighbor contact mapping of the components.
 3. A method asrecited in claim 2, wherein the forward nearest-neighbor contact mappingevaluates distance from one or more additional components of the contactto predicted component positions of the components.
 4. A method asrecited in claim 3, wherein the reverse nearest-neighbor contact mappingevaluates distance from the predicted component positions to the one ormore additional components of the contact.
 5. A method as recited inclaim 2, wherein the reverse nearest-neighbor contact mapping isinitiated when unmapped components remain after the forwardnearest-neighbor contact mapping.
 6. A method as recited in claim 5,wherein mapped component associations that are mapped by the forwardnearest-neighbor contact mapping are released when the reversenearest-neighbor contact mapping is initiated.
 7. A method as recited inclaim 1, further comprising: assigning a same identifier to thecomponents that correlate to the contact; determining that subsequentcomponents correlate to the contact based on the multi-passnearest-neighbor contact mapping; and assigning the same identifier tothe subsequent components that combine with the components to representthe tracking of the contact.
 8. A method as recited in claim 1, furthercomprising: predicting a component position of the contact from thetracking of the contact; and correlating the predicted componentposition to a subsequent component of the contact.
 9. A method asrecited in claim 8, wherein the predicted component position ispredicted based on the components that represent the tracking of thecontact.
 10. A computing device, comprising: a touch-screen display; atouch input module configured to recognize touch input sensor data as aseries of components of a contact on the touch-screen display; at leasta memory and a processor to implement a contact tracking serviceconfigured to: determine that the components correlate to the contactbased on multi-pass nearest-neighbor contact mapping; and associate thecomponents to represent a tracking of the contact.
 11. A computingdevice as recited in claim 10, wherein the multi-pass nearest-neighborcontact mapping includes forward nearest-neighbor contact mapping of thecomponents and reverse nearest-neighbor contact mapping of thecomponents.
 12. A computing device as recited in claim 11, wherein theforward nearest-neighbor contact mapping evaluates distance from one ormore additional components of the contact to predicted componentpositions of the components.
 13. A computing device as recited in claim12, wherein the reverse nearest-neighbor contact mapping evaluatesdistance from the predicted component positions to the one or moreadditional components of the contact.
 14. A computing device as recitedin claim 11, wherein the reverse nearest-neighbor contact mapping isinitiated when unmapped components remain after the forwardnearest-neighbor contact mapping.
 15. A computing device as recited inclaim 14, wherein mapped component associations that are mapped by theforward nearest-neighbor contact mapping are released when the reversenearest-neighbor contact mapping is initiated.
 16. A computing device asrecited in claim 10, wherein the contact tracking service is furtherconfigured to: assign a same identifier to the components that correlateto the contact; determine that subsequent components correlate to thecontact based on the multi-pass nearest-neighbor contact mapping; andassign the same identifier to the subsequent component that representthe tracking of the contact.
 17. A computing device as recited in claim10, wherein the contact tracking service is further configured to:predict a component position of the contact from the tracking of thecontact; and correlate the predicted component position to a subsequentcomponent of the contact.
 18. A computing device as recited in claim 17,wherein the contact tracking service is further configured to predictthe component position based on the components that represent thetracking of the contact.
 19. A method, comprising: recognizing touchinput sensor data as a series of components of one or more contacts on atouch-screen display; initiating a forward nearest-neighbor contactmapping to determine the components that correlate to the respective oneor more contacts; determining that unmapped components remain after theforward nearest-neighbor contact mapping; and initiating a reversenearest-neighbor contact mapping to determine the components thatcorrelate to the respective one or more contacts.
 20. A method asrecited in claim 19, further comprising: releasing mapped componentassociations that are mapped by the forward nearest-neighbor contactmapping when said initiating the reverse nearest-neighbor contactmapping.